I'm a new user with Turbomole and COSMOtherm. I'm working on the Henry's law coefficients (HLC), as mentioned in the title. To obtain these later I have followed the Turbomole tutorial V 7.0 and especially the chapter 6 (Single Point Calculations) with the benzene. Then I have generated the .energy file (with t2energy) and .ccf file (with cosmoprep). With COSMOtherm I have obtained 2.755087E-3 MPa for the HLC. Then, I have redone the calculation with the geomtrical optimization at each step and I have obtained 1.024E-2 MPa. Then, I have done the calculation with the COSMOtherm data base and I have obtained 1.032E-2 MPa. Finally, I have compared to the literature (Sander's data base) and I must have approximatively 30 MPa. In COSMOtherm, I have selected TZVP as level, pure benzene, 1L gas/ 1L solvent, 25°C as temperature and mole fraction option. Have I made a mistake somewhere?

The Turbomole calculation seems to be OK. You should, however, always try to be fully consistent with the quantum chemical level chosen in COSMOtherm. I.e. you should use geometry optimized BP-TZVP cosmo- and energy-files, not single points.

But it seems that you have computed the Henry law constant of benzene in itself (which is nothing else than the vapor pressure Pvap/RT ). The experimental value of 30 MPa you use as comparison is the Henry law constant of benzene at infinite dilution in solvent water(!). Thus you are comparing different properties.

To obtain a correct prediction, you have to load benzene and water into the job, and then, in the Gsolv/Henry panel, set pure water as "Solvent". This will give you kHenry = 25.1 MPa with the current version (1601, TZVP parametrization) , which is much closer to the experiment.